Drop formation method and device using a cavity with a degraded quality factor

Abstract

A drop generator for a printing head of a continuous inkjet printer includes at least one ink feed conduit for feeding ink into a stimulation chamber, which has a quality factor Q lower than 2 and at least one resonant frequency f r ; an actuator for stimulating a wall of said stimulation chamber; and at least one nozzle for ejecting a jet.

What is claimed is: 
     
       1. A drop generator for a printing head of a continuous inkjet printer, including:
 at least one ink feed conduit for feeding ink into a stimulation chamber, which has a quality factor Q lower than 2 and at least one resonant frequency f r , wherein the quality factor is a ratio of the resonant frequency f r , to a full width half maximum of a frequency peak of the resonant frequency f r , 
 an actuator for stimulating a wall of said stimulation chamber; and 
 at least one nozzle for ejecting a jet. 
 
     
     
       2. The drop generator according to  claim 1 , including a layer which dampens the oscillations of the actuator transmitted to the cavity. 
     
     
       3. The drop generator according to  claim 2 , said layer, which dampens oscillations, being of Kapton. 
     
     
       4. The drop generator according to  claim 1 , at least one part of the cavity being of annealed stainless steel. 
     
     
       5. The drop generator according to  claim 1 , said actuator being able to apply to said stimulation chamber stimulation signals separated by a time duration between 5μs and 40μs. 
     
     
       6. The drop generator according to  claim 1 , said actuator being able to apply to said stimulation chamber stimulation signals, the spectrum of which includes at least said resonant frequency f r . 
     
     
       7. The drop generator according to  claim 1 , said resonant frequency f r  being between 50kHz and 300kHz. 
     
     
       8. The drop generator according to  claim 1 , said stimulation chamber having:
 a length between 6000 μm and 500 μm; 
 a width between 2500 μm and 200 μm; 
 a thickness between 600 μm and 10 μm. 
 
     
     
       9. The drop generator according to  claim 1 , said stimulation chamber having a volume between 10 mm 3  and 10−3 mm 3 . 
     
     
       10. A multi-jet printing head of a continuous inkjet printer including:
 a plurality of nozzles for forming jets, each nozzle being associated with a drop generator according to  claim 1 ; 
 at least one electrode for deviating each jet; 
 an outlet slot, open outwardly of the printing head and enabling the drops or ink segments for printing to flow out; 
 a gutter for recovering the drops or segments which are not intended for printing. 
 
     
     
       11. The printing head according to  claim 10 , further including at least one pump allowing, for at least one ink viscosity between 1 cps and 20cps, a jet velocity, said jet having a pass band, the cut-off frequency (F c ) of which is higher than the resonant frequency f r . 
     
     
       12. A continuous inkjet printer including the printing head according to  claim 10 , and further including a controller programmed to apply at least 2 successive cut-offs to a jet, for creating at least one drop isolated from the rest of the jet, this at least one drop being preceded by an ink segment and followed by another ink segment. 
     
     
       13. The continuous inkjet printer according to  claim 12 , said controller being programmed to apply 3 or more successive cut-offs to a jet, for creating a series of at least 2 drops, this series of drops being preceded by an ink segment and followed by another ink segment. 
     
     
       14. The continuous inkjet printer according to  claim 12 , said controller being programmed to form ink segments, preceding or following said drops, having a length of, at least, between 400 μm and 1200 μm. 
     
     
       15. A method for forming at least one individual drop using the multi-jet printing head according to  claim 10 , wherein:
 at least 2 successive cut-offs are applied to a jet, thus creating at least one drop isolated from the rest of the jet, this at least one drop being preceded by an ink segment and followed by another ink segment; 
 or at least 3 or more successive cut-offs are applied to a jet, thus creating a series of at least 2 drops, this series of drops being preceded by an ink segment and followed by another ink segment. 
 
     
     
       16. The method according to  claim 15 , said ink segments, preceding or following said at least one drop, or said series of at least 2 drops, having a length of, at least, between 400 μm and 1200 μm. 
     
     
       17. The method according to  claim 15 , wherein:
 at least one jet having a cut-off frequency (F c ) higher than the resonant frequency f r  of the corresponding cavity is produced, 
 at least one activation signal, the spectrum of which includes at least said resonant frequency f r , is applied to the actuator. 
 
     
     
       18. A drop generator for a printing head of a continuous inkjet printer, including:
 at least one ink feed conduit for feeding ink into a stimulation chamber, which has a quality factor Q lower than 2 for at least one resonant frequency f r , wherein the quality factor is a ratio of the resonant frequency f r , to a full width half maximum of a frequency peak of the resonant frequency f r , 
 a stimulator for stimulating a wall of said stimulation chamber; and 
 at least one nozzle for ejecting a jet. 
 
     
     
       19. The drop generator according to  claim 18 , including a layer which dampens the oscillations of the stimulator transmitted to the cavity. 
     
     
       20. The drop generator according to  claim 19 , said stimulator being able to apply to said stimulation chamber stimulation signals separated by a time duration between 5 μs and 40 μs.